Chapter 4 Solubilization by solutions of surfactants

1.Solubilization( 增溶 )  The curve of surface tension  E.g. 5 g of ethylbenzene( 乙苯 ) which is normally insoluble in water, may be dissolved in 100ml of a 0.3 M aq. Solution of potassium hexadecanoate ( 棕榈酸钾 ) to yield a clear solution.  Solubilizer – 增溶剂 potassium hexadecanoate  Solubilizate – 增溶质 ethylbenzene

 C > CMC micellar  No hydrotropy ( 水溶助长性 ) No micellar and micellar solution  No emulsifying Multiphase and homogeneous phase Thermodynamics unstable system and dynamics stable system  Thermodynamics stable system Spontaneous process ( 自发过程 )  Homogeneous phase system (transparent)  Dynamic equilibrium system – average residence time of various additives in micelles – sec

2. Mechanisms of solubilization (1) In the micellar core – 夹心型加溶 solubilizate - nonpolarity components saturated hydrocarbon (2) At the core/palisades interface – 栅栏型加溶 polarity components such as fatty acids, amines, alcohols, and esters.

(3) On the micelle surface – 胶束表面加溶 (see (d)) poly-functional group additives such as glycerin( 甘 油 ), cane sugar, and some dyes (4) In the palisades layer of POE chains – POE 链间 加溶 (see (c) ) such as aniline( 苯胺 ), phenol( 苯酚 ) Solubilization capacity( 增溶量 ) 4 > 2 > 1 > 3

3. Factors affecting the solubilization (1)Surfactants structure (a)Hydrophobic groups R  CMC , n , solubilization capacity  branching degree , CMC , solubilization capacity  degree of un-saturation , CMC , solubilization capacity 

(b) Hydrophilic groups CMC: nonionics < anionics  cationics solubilization capacity: nonionics > cationics > anionics P(OE) m nonionics: m , cmc , n , solubilization capacity  (2) The solubilization capacity of solubilizate (a)Liquid > Solid (b)Short chain > Long chain

(c) Cycloparaffin > Linear chain (d) Polarity > Nonpolarity (e) Unsaturated hydrocarbons > Saturated hydrocarbons benzene > cyclohexane( 环己烷 ); but, tetraphene( 丁苯 )> naphthalene( 萘 ). (3) The effect of other additives (a)Other solubilizates Same type – solubilization capacity  Different type - solubilization capacity 

The mechanism for increased solubilization of nonplar addiyives in the presence of polar additives

Maximum additive concentration(MAC) solubilized in 1% aqueous solution of C 10 H 21 (OE) 10 CH 3 nonionics at 27°C

Maximum additive concentration(MAC) solubilized by typical ionic surfactants

(b) The effects of added electrolyte  ionics: I , CMC , n , MAC in core  ; MAC at the core/palisades interface .  nonionics: I , CMC , n , solubilization capacity  (c) Surfactants  homologous compound – no synergism  different type – synergism e.g. anionics & cationics: MAC in core , at the core/palisades .

(4) The effect of temperature (a)Ionics: the effect of temp. on CMC is small. but if T , the solubility of solubilizates in micelle , solubilization capacity . (b)POE nonionics:  nonpolarity solubilizates T , CMC , n , MAC in core   polarity solubilizates T , CMC , n , MAC at the core/palisades  ; if T , (OE) dehydration, MAC at the core/palisades 

The effect of temperature on the CMC, n,and Solubilization capacity of methoxydodecaoxy- ethylene decyl ether (CH 3 O(C 2 H 4 O) 12 C 10 H 21 )

Micellar catalysis in aqueous solvent Proposed mechanisms for the catalytic (and retarding) effects of micelles in organic reactions

Mechanism of Emulsion Polymerization